The subject invention relates to the fabrication of metal oxide patterns on a substrate adapted for use with thin film inductive transducers. The transducers, commonly referred to as thin film magnetic heads, are useful for recording and reading magnetic transitions on a moving magnetic recording medium.
Thin film recording heads are generally manufactured by an etching process wherein an electromagnet is formed on the surface of a substrate. More particularly, a magnetic material is deposited on a suitable substrate and is etched to the desired configuration. Thereafter, conductive layers are deposited on the magnetic material and etched to define the windings of the electromagnet. At least one additional layer of magnetic material is deposited in a manner such that the rear ends of the magnetic materials are connected while the front ends thereof are separated to define a recording gap. An electric current may be passed through the windings of the conductor for recording.
The gap or pole tip region of the head is intended to fly in close proximity to the magnetic recording medium. In order to maximize the reading and writing ability of the thin film head, it is of critical importance to define the geometry of the pole tip region to within extremely precise tolerances. It has been found that read/write errors can be minimized when the pole tip regions of the electromagnet are formed with straight side walls.
In contrast, the side walls of the remaining portions of the magnetic head, which are spaced from the pole tip region, need not be formed with a precise vertical geometry. In fact, when the lower pole of the head is provided with vertical side walls along its entire length, problems arise relating to the deposition of the conductive layer used to define the windings of the electromagnet. As can be appreciated, it is relatively difficult to control the thickness of a layer which is being deposited on a surface having sharp, angular features. Thus, windings deposited on the magnetic material will frequently have undersirable discontinuities particularly in regions having sharp corners.
Accordingly, in the prior art, various methods have been developed to reduce the occurance of discontinuities in the windings. One proposed solution is to bevel the side walls of the magnetic material to obtain a smooth, sloping surface thereby facilitating the deposition of the conductive layer over the magnetic material. However, it is important that only the rear portions of the magnetic material be beveled since the pole tip regions of the head must be provided with vertical side walls in order to minimize read/write errors.
Therefore, in the prior art, a method was developed wherein the degree of beveling of the side walls could be controlled such that the pole tip regions were provided with vertical side walls, while the rear portions of the side walls were sloped to facilitate the deposition of the conductive windings. The later method is disclosed in U.S. Patent Application Ser. No. 311,968 filed Oct. 16, 1981, (now issued as U.S. Pat. No. 4,351,698) assigned to the assignee as the subject invention. The latter method includes a new and improved multiple masking technique to achieve the unique and desired configuration of the magnetic material.
Various other solutions have been proposed to solve the problem of discontinuities in the conductive layer. One such solution, called "planarization", includes filling in the areas, adjacent the magnetic material, with a non-magnetic, non-metallic compound in a manner such that the top surface of the resulting structure is defined by a smooth plane. In this solution, the magnetic material is formed with vertical side walls throughout its construction. Further, since the upper surface of the magnetic material is co-planar with the non-magnetic filler material, additional layers may be accurately deposited on the planar surface of the structure whereby discontinuities may be substantially diminished.
Unfortunately, in the prior art, no suitable method has been devised to produce the proposed planarized structure. The most obvious method would include a mechanical lapping operation. More particularly, in the latter method, the metallic material is initially deposited on a substrate. Thereafter, a layer of non-metallic, non-magnetic filler material is deposited over the magnetic material. Using a mechanical grinder or lapping apparatus, the surface of the layers could be abraded until the desired planar configuration is achieved. However, due to the fragile nature and small size of thin film magnetic recording heads, this method is impractical because it is both cumbersome and expensive.
Another proposed planarization method includes a thermal oxidation step, for equalizing the depth of the layers. Thermal oxidation is a diffusion process which typically takes place at elevated temperatures in the range of 950 to 1200 degrees centigrade. This method is not adaptable to present manufacturing requirements since the materials utilized in forming the thin film magnetic heads suffer severe degredation, including recrystalization and strain, when subjected to temperatures over 400 degrees centigrade. Another possible method includes the use of liquified glasses, which can be flowably formed on the substrate. However, as with thermal oxidation, most usable glasses melt at temperatures greater than 400 degrees centigrade. The glasses which are found to melt at lower temperatures are not compatible with thin film processing because their thermal expansion and softening points are not satisfactory. Accordingly, it would be desirable to provide a new and improved method for planarizing the surface of the magnetic material of a thin film recording head such that successive layers may be readily deposited without discontinuities.